Many parts of the world are presently threatened by the spread of new, deadly, and contagious diseases, such as severe acute respiratory syndrome (SARS), or the possibility of terrorist attacks with biological weapons. Travelers may spread dangerous microbes intentionally or unintentionally. The screening technologies that detect guns, knives, or explosives are of little value against these new biological hazards. Standard medical diagnostic techniques are time-consuming and unsuited for mass screening at places such as airports, ports of entry, immigration stations, crowded malls, or places of business. The present invention provides the ability to screen the masses for diseases characterized by the presence of a fever or elevation in body temperature.
Extreme temperatures may overcome the thermoregulatory system of the body. Physical exertion under hot humid conditions may result in heat stroke, which is characterized by a dangerous rise in core body temperature. Exposure to extreme cold temperatures may result in hypothermia, which is a dangerous decrease in core body temperature. The present invention provides an approach to remotely and noninvasively monitoring body temperatures during exposure to extreme ambient temperatures so that medical intervention may occur in a timely manner.
Animal diseases such as chronic wasting disease (CWD), mad cow disease, scrapies, and West Nile Virus all exhibit thermoregulatory components. The present invention is valuable as part of a noninvasive and remote screening regimen for these diseases.
According to the Center for Disease Control (CDC), severe acute respiratory syndrome (SARS) is a respiratory illness that has recently been reported in Asia, North America, and Europe. In general, SARS begins with a fever greater than 100.4° F. [>38.0° C.]. Other symptoms may include headache, an overall feeling of discomfort, and body aches. Initially, some people experience mild respiratory symptoms. After 2 to 7 days, SARS patients may develop a dry cough and have difficulty breathing. In 10-20% of cases, the respiratory illness is severe enough to require intubation and mechanical ventilation. The mortality rate is reported to be 20% for those under age 60 and 40% for those over age 60.
SARS appears to be spread by close person-to-person contact. Most cases of SARS have involved people who have cared for a SARS patient or had direct contact with infectious material such as respiratory secretions. SARS may be acquired by a healthy individual if that individual touches the skin of an infected person or objects which are contaminated with infectious droplets and then in turn touches the eye(s), nose or mouth of the healthy individual. This can readily happen when a person, sick with SARS, coughs or sneezes droplets onto themselves, other people or nearby surfaces. SARS may also be spread more broadly through the air or by other ways not yet known.
According to Dr. J. Gerberding, director for the Centers for Disease Control and Prevention, the SARS virus can quickly get out of control. It is necessary to take all steps to detect new cases and isolate them in the hospital or at home until the contagious period has passed. While it is very important to pursue a vaccine, this virus will not likely be eradicated soon.
The criteria presently used to detect new cases and screen subjects for SARS include: an elevated temperature greater than 100.4° F. (38.0° C.), a dry persistent cough, and travel to an area of known SARS presence or exposure to a known SARS patient.
Since an elevated temperature greater than 100.4° F. (38.0° C.) is one of the earliest indicators for SARS, clinicians and government leaders are looking to thermal measurement techniques as screening tools to limit the transmission of the disease and to identify potential SARS subjects via mass screening at public sites such as airports, ports of entry, immigration stations, crowded malls, or places of business. Many levels of government (Federal, State, and local) have the authority to require the isolation of sick persons to protect the general public.
In addition to SARS, many other diseases or conditions have a change in body temperature as an indicator. Additionally, numerous infectious diseases, conditions associated with biological weapons, and heat stroke may be indicated by an increase in body temperature. Hypothermia from exposure or surgery may also be accurately detected by a decrease in body temperature.
Additional examples of diseases for which mass screening may be advantageous include viral agents such as smallpox, Ebola hemorrhagic fever, Lassa fever, Congo fever, viral hemorrhagic fever, Enteric fever, Meningococcal infection, tuberculosis, and smallpox. Bacterial agents such as plague may be detected. Screening for preformed biological toxins such as staphylococcal enterotoxin B, ricin, and T-2 Mycotoxin may also be possible.
A review of current clinical methods for measuring body temperature finds no present method is well-suited for rapidly screening large numbers of people. Body temperature is commonly measured by either oral, rectal, axillary or tympanic methods. Oral temperatures are obtained by placing a clinical thermometer under the tongue for 2-3 minutes with a normal reading of 98.6° F. Rectal temperatures are obtained by placing a thermometer at least 1½ inches (3.75 cm) into the anal canal for 3-5 minutes with a normal reading 0.5 to 1.0° F. above oral temperatures. Axillary temperatures are obtained by placing a thermometer under the armpit while placing the arm tightly against the body with normal temperatures approximately 0.5° F. lower than oral temperatures. Eardrum or tympanic temperatures may be obtained via an infrared device placed into the ear canal with normal temperatures similar to oral temperature values. Each of these standard measurement methods requires several minutes to obtain the measurement and/or close personal contact with the patient—significant disadvantages for mass screening of a contagious disease. Additionally, the above methods require the disposal of large volumes of contaminated thermometer sheaths or ear canal adapters.
Since current clinical methods for measuring body temperature are not well-suited for SARS screening, clinicians, scientists, and entrepreneurs are attempting to use thermal imaging for this purpose. In basic principle, thermal imaging can thermally scan an individual patient or large numbers of people rapidly and remotely. Thermal imaging technology can obtain thermal images at a video rate (30 images per second) compared to current clinical methods that take minutes for each measurement. Thermal imaging can also obtain the images from a distance of several feet to hundreds of feet depending upon the optical system employed, thus overcoming the disadvantage of close contact with potentially contagious patients. However, the direct application of thermal imaging, in its present state, to measure body temperature has serious shortcomings.
While it is desired to obtain measurements of core body temperature for each patient via thermal imaging techniques, present thermal imaging techniques provide only a measurement of surface or skin temperatures. In general, skin temperature varies with ambient temperature, anatomical site and circulatory perfusion. For a constant oral temperature of 98.6° F. the skin temperatures may be 96.0, 91.0, and 86.5° F., for ambient temperatures of 90, 70, and 55° F., respectively. The skin temperatures of various anatomical sites such as the nose, ears, cheeks, forehead and eyes may vary by 10-15° F. Cardiovascular dynamics and even psychological variables may also change skin temperatures in such sites as the cheeks, ears or nose.
In addition to the variability of absolute skin temperatures, many of the thermal imaging systems in use today have absolute thermal tolerances that are inappropriate for body temperature measurements. Many thermal imaging systems have tolerances of +/−2° C. (+/−3.6° F.). With such tolerances, a skin temperature of 91.0° F. (ambient temperature, 70° F.), which corresponds to an oral temperature of 98.6° F., could be recorded as a skin temperature of 87.4° F. to 94.6° F. and still remain within the camera tolerances.
Although present thermal imaging technology can provide rapid and remote acquisition of skin temperatures, these skin temperatures cannot provide temperature measurements that are accurately correlated to core body temperatures, regardless of the accuracy of the temperature measurement. Without accurate linkage to core body temperatures, the readings have little clinical significance. The value is limited to the identification of individuals that have higher (or lower) skin temperatures relative to a group of individuals experiencing similar ambient, emotional and exertion conditions at that particular time and location.
Additionally, some manufacturers of thermal imaging systems have added image averaging techniques, alarms for the detection of persons with elevated skin temperatures, color highlighted images for alarm conditions and other features which fall into the category of ‘bells and whistles’. While these features might prove useful when based on accurate core body temperature measurements, they become nuisance alarms when based upon inaccurate or relative indications.
There exists a need to rapidly, remotely and accurately measure core body temperature. This desired technique should exhibit the rapid and remote screening characteristics of present thermal imaging technology coupled with the accurate measurements of body temperature exhibited by present clinical techniques. With such a combination, large numbers of people could be accurately screened for elevated core body temperatures and properly treated or isolated. The present invention addresses these goals.